The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
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Mounjaro vs Wegovy: Which Can Your GP Prescribe?
If you're wondering whether your GP might prescribe Mounjaro or Wegovy for weight management in the UK, it's important to understand how these two prescription medications differ. Both are licensed for weight loss in UK adults, but they work in different ways and have different dosing schedules. Your GP or a specialist weight management service will assess which is more suitable for your individual health needs. Use our free GLP-1 weight loss calculator to explore potential outcomes, and our BMI calculator to understand your starting point.
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Calculate Your BMI Instantly
Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
How Mounjaro and Wegovy Work Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two separate hormone pathways in the body. This dual mechanism may help regulate appetite, reduce cravings, and support feeling fuller after meals more effectively than single-pathway medications.
Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single hormone pathway. Both medications slow gastric emptying and reduce appetite, but Mounjaro's dual action may offer a different effect profile.
Dosing differences: Mounjaro starts at 2.5 mg once weekly and titrates up to a maximum of 15 mg. Wegovy starts at 0.25 mg and reaches a maximum of 2.4 mg once weekly. Clinical trial data showed Mounjaro achieved approximately 15–21% average body weight loss, while Wegovy showed around 14.9% average loss. Individual results vary significantly, and your prescriber will consider which approach suits your health profile.
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How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Clinical Evidence and GP Decision-Making
Your GP's recommendation will depend on SURMOUNT trial data (Mounjaro) versus STEP trial data (Wegovy), your medical history, side effect tolerance, and NHS or private access routes. Both medications require a prescription and clinical assessment before being dispensed. Access through the NHS typically involves referral to a tier 3 specialist weight management service, whilst private prescription is available through registered online services following an online clinical assessment.
Neither medication is assured to produce weight loss, and both work best alongside a reduced-calorie diet and increased physical activity. Your prescriber will explain the eligibility criteria, potential side effects, and realistic outcomes before starting either treatment.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Can my GP prescribe Mounjaro or Wegovy directly?
GPs can prescribe both, but in the NHS, prescription weight loss medications are typically initiated through specialist tier 3 weight management services rather than standard GP practices. Private prescription is available through GPhC-registered online pharmacies following a clinical assessment. Your GP can refer you to NHS specialist services or advise on private options.
What's the main difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP+GLP-1 agonist (two hormone pathways), while Wegovy is a GLP-1 agonist only (one pathway). Mounjaro typically offers higher average weight loss (15–21%) versus Wegovy (around 14.9%), though individual results vary. Your prescriber will consider which mechanism suits you best.
Which medication causes fewer side effects?
Both have similar common side effects: nausea, diarrhoea, vomiting, and constipation. Individual tolerance varies considerably. Your prescriber will discuss side effect profiles and monitor you during treatment. Starting doses are low and increased gradually to minimise side effects.
How long does it take to see weight loss results?
Weight loss typically begins within 2–4 weeks of starting either medication, though the first few weeks focus on dose adjustment. Significant results are usually seen over 12–16 weeks. Progress is not linear — some people lose steadily, others plateau then lose more. Track your journey with our free progress tracker.
Do I need to change my diet and exercise while on these medications?
Yes. Both Mounjaro and Wegovy work best when combined with a reduced-calorie diet and regular physical activity. These medications support appetite control, but they don't replace the need for lifestyle changes. Your prescriber will discuss realistic expectations and sustainable behaviour change strategies.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.